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Streptococcus viridans: Wikis


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Streptococcus viridans-group
Scientific classification
Kingdom: Bacteria
Phylum: Firmicutes
Class: Bacilli
Order: Lactobacillales
Family: Streptococcaceae
Genus: Streptococcus

Viridans Streptococcus is a pseudo-taxonomic non-Linnaenan term for a large group of commensal streptococcal bacteria that are either α-hemolytic, producing a green coloration on blood agar plates (hence the name "viridans", from Latin "vĭrĭdis", green), or non-hemolytic. They possess no Lancefield antigens.[1]

In general, pathogenicity is low.[2]



Viridans streptococci can be differentiated from Streptococcus pneumoniae using an optochin test, as Viridans streptococci are optochin resistant; they also lack either the polysaccharide-based capsule typical of S. pneumoniae or the Lancefield antigens of the pyogenic members of the genus.[3]

Viridans streptococci Streptococcus pneumoniae
Solubility in bile Insoluble Soluble
Fermentation of inulin Not a fermenter Fermenter with acid production
Sensitivity to optochin Not sensitive Sensitive
Pathogenicity to mice Non pathogenic Pathogenic
Quellung test Negative Positive


The organisms are most abundant in the mouth and one member of the group, S. mutans, is the etiologic agent of dental caries. Others may be involved in other mouth or gingival infections.

If they are introduced into the bloodstream they have the potential of causing endocarditis, particularly in individuals with damaged heart valves. They are the most common causes of subacute bacterial endocarditis.

They can also cause necrotizing fasciitis.



  1. ^ Ryan KJ, Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. pp. 293–4. ISBN 0838585299.  
  2. ^ MeSH Viridans+Streptococci
  3. ^ Patterson MJ (1996). "Streptococcus". Baron's Medical Microbiology (Baron S et al., eds.) (4th ed.). Univ of Texas Medical Branch. ISBN 0-9631172-1-1.  


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